In the operation of a refrigeration unit, such as a freezer, it is often critical that the contents thereof, food for example, be kept below a certain temperature. This may be necessary, for example, to avoid spoilage of food.
When a refrigeration unit fails to function correctly, whether as a result of a power failure or some other cause, the air inside the unit is not kept sufficiently cool. Freezer and refrigerator alarms have been developed which measure air temperature within the unit and initiate an alarm should the temperature rise above a certain level. U.S Pat. 5,262,758 (Nam et al.) and U.S. Pat. 4,490,986 (Paddock) each disclose a system in which an alarm is initiated only after a certain air temperature has been exceeded for a certain length of time.
However, generally speaking, the temperature of the air inside the refrigeration unit is of secondary concern. The primary concern is that the temperature of the contents of the unit not rise above a critical level. But, these alarm delays do not take into account a number of other factors which may affect the temperature of the contents, such as the amount by which the air temperature inside the unit exceeds a critical level or the temperature of the contents, or the quantity of contents inside the freezer.